1. Field of the Invention
The present invention relates to a method and a device for synchronously controlling multiple printing presses or multiple units in a printing press suitable for application to web-fed rotary printing presses.
2. Description of the Related Art
Conventionally, a synchronous drive control device for synchronously driving multiple printing presses or multiple units (such as printing units or folding machines) in a printing press has been configured to perform synchronous control even when the printing press or the printing presses are in shutdown as shown in Japanese Unexamined Patent Publication No. 2001-309681 (hereinafter, referred to as Patent Document 1), for example.
That is to say, Patent Document 1 relates to a synchronous control device applicable to web-fed rotary printing presses and the like, and more specifically, discloses an invention concerning a synchronous control device including a home position aligning function configured to accurately achieve synchronous drives of rotation phases and rotation speeds in terms of either electric motors including a main motor and a plurality of sub motors or respective machine shafts to be driven by the electric motors. Upon the synchronous control, firstly, phases of an electric motor shaft and the machine shaft of the main motor are constantly detected with a phase detector by use of an output from a rotary encoder of the main motor and an output from a main motor machine shaft home position detector. Meanwhile, phases of electric motor shafts and the machine shafts of the sub motors are constantly detected with phase detectors by use of outputs from rotary encoders of the sub motors and outputs from sub motor machine shaft home position detectors. Then, phase differences between the machine shaft of the main motor and the machine shafts of the sub motors are obtained by use of a machine shaft phase difference detector, and phase differences between the electric motor shaft of the main motor and the electric motor shafts of the sub motors are obtained by use of an electric motor shaft phase difference detector. Based on these outputs, home positions of the machine shafts of the main motors and the sub motors are aligned and then home positions of the electric motor shafts of the main motor and sub motors are aligned to perform synchronous control of the main motor and the sub motors.
However, the invention according to Patent Document 1 is configured to perform the synchronous control (position control and “0” speed control of the electric motors) even when the web-fed rotary printing press are in shutdown. Accordingly, currents will flow on the electric motors and electric motor drive circuits even when the printing presses are in shutdown. For this reason, this invention has problems of an increase in power consumption, and of deterioration in durability of the electric motors and bearings of the electric motors which are attributable to deterioration of greases of the electric motors of the bearings of the electric motors caused by heat generation.